<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title></title>
  </head>
  <style>
    .body {
      height: 100px;
      width: 100px;
      background-color: blue;
      /*相对位置*/
      position: relative;
      /*无用代码*/
      margin: 100px 100px;
    }
    .triangle5 {
      width: 0;
      height: 0;
      border: 10px solid red;
      border-left-color: transparent;
      border-top-color: transparent;
      position: absolute;
      bottom: 0px;
      right: 0px;
    }
  </style>
  <body>
    <div class="body">
      <div class="triangle5"></div>
    </div>
  </body>
</html>
